1. Field of the Invention
The present invention relates to a light emitting diode, and more particularly, to a light emitting diode having extensions of electrodes for current spreading.
2. Discussion of the Background
Gallium nitride (GaN) based light emitting diodes have been applied and developed over about a decade. The GaN based LEDs have significantly changed LED technology and are currently used in a variety of applications such as full color LED display, LED traffic signals and white LEDs. In recent years, high-efficiency white LEDs are expected to substitute for fluorescent lamps. In particular, the efficiency of the white LEDs almost approaches that of a typical fluorescent lamp.
In general, a gallium nitride based light emitting diode is formed by growing epitaxial layers on a substrate such as a sapphire substrate, and has an N-type semiconductor layer, a P-type semiconductor layer, and an active layer interposed therebetween. Meanwhile, an N-electrode is formed on the N-type semiconductor layer, and a P-electrode is formed on the P-type semiconductor layer. The light emitting diode is driven while being electrically connected to an external power supply via the electrodes. At this time, a current flows from the P-electrode to the N-electrode via the semiconductor layers.
Since a typical P-type semiconductor layer has high resistivity, there is a problem in that a current is not evenly spread in the P-type semiconductor layer but is concentrated on a portion where the P-electrode is formed and intensively flows through corners. The current concentration leads to reduction in a light-emitting region and consequently degrades luminous efficiency. To solve these problems, a technique of forming a transparent electrode layer having low resistivity on a P-type semiconductor layer for current spreading has been used. A current introduced from the P-electrode spreads in the transparent electrode layer and flows into the P-type semiconductor layer. Thus, the light emitting region of the light emitting diode can be enlarged.
However, the transparent electrode layer has a restricted thickness because of its light absorption, causing a limitation on current spreading. In particular, the current spreading using the transparent electrode layer has a limitation in a light emitting diode with a large area of about 1 mm2 or more used for high output power.
Meanwhile, the current flows through the semiconductor layers toward the N-electrode. Accordingly, the current is concentrated on a portion of the N-type semiconductor layer where the N-electrode is formed. This means that the current flowing in the semiconductor layer is concentrated in the vicinity of a region formed with the N-type electrode. Accordingly, there is a need for a light emitting diode capable of solving a problem of current concentration in an N-type semiconductor layer.